Solaris - (Sun Microsystems) Sun Unix-based user environment, including the Unix operating system and an X11-based window system. Solaris 1.x is a retroactive (marketing?) name for SunOS4.1.x, a BSD-like version of Unix with some SVR4 features. Solaris 2.x (which is what most people mean by "Solaris") includes SunOS5.x, which is an SVR4-derived Unix.